"왜 그런 일이 생겼는지 몰라." You're saying you don't know why that kind of thing happened in a direct, plain way. "왜 그런 일이 생긴 것인지 몰라." I agree that this puts emphasis on "happen". But still, "왜 그런 일이 생긴 건지 몰라", which is much more common in spoken Korean, sounds indirect unlike the above. 거 is a modal and versatile noun. Saying "...건지 몰라", you're seeing it as the whole picture like seeing the forest instead of the trees, rocks etc. EDIT : 왜 그런 일이 생긴 것인지 몰라 is just a bit more formal than the last one. "왜 그런 일이 생긴 건지 모르겠어" is more commonly used.

It means "Don't know why did that thing happen" "생겼는지" and "생긴 것인지" is the same meaning. It means "happened" or "did happen"

hi! I think these are same but the latter is emphasize the meaning. I mean, that is emphasize "happen" this word. I really don' t know ' why happend ' that kind of affair. sorry my English is not good so I don't know how to explain.